The invention relates to a method for feeding pasty masses using a pump device which has a piston pump with at least two cylinders, each cylinder having one piston, with each cylinder being connected via an inlet opening to a pre-fill container and with each cylinder being connected via an outlet opening to a feed line. The invention also relates to a pump device for feeding pasty masses with a piston pump having one cylinder, which has a piston and which is connected with a pre-fill container via an inlet opening that can be closed by an inlet slide valve.
When feeding concrete, pump devices are used which are typically constructed from piston pumps having two cylinders, with each cylinder having a piston. The cylinders receive the pasty mass to be transported from a pre-fill container in a so-called suction stroke and then feed the suctioned pasty mass to a feed line connected to the piston pump in a so-called pump stroke. The pistons of the two cylinders are operated in opposite direction in order to feed the pasty mass to the feed line with the greatest attainable uniformity. The feed line of such pump device can have a substantial length. It is frequently part of a crane boom and is used to feed the pasty mass from the location of the pump device to remote ends of the construction site. Due to the length of the feed line, very small interruptions in the feed flow of the pasty mass can already cause significant swinging movements of the feed line due to the mass inertia. It is therefore desirable to develop a method which allows a continuous feed of the pasty mass.
Methods for feeding pasty masses supposedly continuously are known from practical applications. However, when analyzing the feed path of the pasty mass from the interior space of the cylinder, from which it is pressed by the piston, to the outlet end of the feed line, it becomes clear that although these methods used in practice are capable to provide improved uniformity of the transport, the transport is not continuous. Components, in particular valves, are arranged in the feed path of these pump devices, wherein the valve bodies are in a closed position arranged at a position where they displace the pasty mass, whereas in an open position the valve body is removed from the feed space provided for feeding the pasty mass. Accordingly, the feed flow is interrupted during each opening operation. This interruption is filled by the pasty mass which is already downstream of this gap and falls back. This adversely affects the uniform feed of the pasty mass in the feed direction, so that the pasty mass cannot be viewed as being fed continuously.
A truly continuous feed of concrete is achieved with a 2-cylinder piston pump disclosed in DE 42 08 754 A1. However, the opening of the swivel pipe (there: 104) and, on one hand, the slide valve plates (there: 101, 102) attached to the sides thereof and, on the other hand, the so-called orifice plate, on which the opening of the swiveling pipe with the slide valve plates sealingly slides, experience unacceptably high wear. It became clear that switching under load with this arrangement caused the following unsolved problems:
1) The abrasive, fine-grain components of the concrete were pressed during the switching process by the continuously maintained feed pressure into the sealing gaps, where they then produced a high switching resistance of the slide valve which furthermore caused significant wear due to the very long switching paths of the slide valve which is unknown with conventional discontinuous pumps.2) Point 1) requires a very high drive power, i.e., requires a very high switching power over a longer time.
A continuously feeding 2-cylinder concrete pump with a total of two slide valves was proposed in the patent application which matured into EP 1 003 909 B1, wherein one slide valve switches at “equilibrium pressure” whereas the other slide valve switches at “zero pressure.” In the slide valve switching at equilibrium pressure, the same pressure as is permanently present outside the pivoting pipe in the pressure housing and the attached feed line is also produced inside the pivoting pipe before the switching operation by compressing the suctioned concrete. Accordingly, there is no pressure difference between the inside and the outside on the mouth of the pivoting pipe sliding along the inside of the pressure housing. Fine, abrasive components of the concrete are therefore not pressed into the slide gaps by a hydrostatic pressure difference. Instead, a state exists which is very similar to an unpressurized state.
The shutoff valves in the suction line from the pre-fill container to the pivoting pipe only opens the concrete due has relaxed in the suction stroke and closes before compression of the suctioned concrete. This suction slide valve therefore switches without hydrostatic pressure in the concrete (“zero pressure”). These remarkable advantages of the configuration described in EP 1 003 909 B1 are to be contrasted with the following disadvantages:
The pressure housing is very large, and very heavy with a presently typical maximum concrete pressure of about 90 bar, making cleaning very complex. Particularly disadvantageous are the tight bends which the concrete has to traverse during the pump stroke past the suction-swiveling pipe through the concrete residing in the pressure housing on its path to the feed line. This pump is therefore unable tool feed very coarse-grain concrete mixtures. Another disadvantage is that when switching to the other cylinder, the mouth of the swiveling pipe must be accommodated between the two cylinder openings. This necessitates a large center spacing between the two feed cylinders, so that these two cylinders cannot be installed at an angle extending between the side rails of the support vehicle, as would be required for a sufficiently low fill height of the pre-fill container.
DE 10 2005 008 938 B4 also includes a total of 2 slide valves which operate with both feed cylinders. One slide valve is hereby a four-way slide valve with two switch positions switching at “zero pressure”, e.g., the swiveling pipe in an open pre-fill container presently used with discontinuous pumps. An additional shutoff gate valve is installed in the feed line which always switches at equilibrium pressure. The substantial improvement of DE 10 2005 008 938 B4 over EP 1 003 909 B1 is, inter alia, that the switching process not only takes place under equilibrium pressure and/or zero pressure, but that an automatic ring can be used at least with the shutoff valve switching at equilibrium pressure, wherein the hydrostatic contact pressure of the automatic ring is compensated by the pressure of the concrete at equilibrium pressure, because the same pressure is present on the outside and the inside on the cutting ring after compression. The contact face of the cutting ring with its sliding partner, the swiveling body, it is therefore also subjected to the pressure of the medium as gap pressure, which exerts on the cutting ring a force of equal magnitude opposing the hydrostatic contact pressure. For the contact pressure during the switching process, ideally only the much smaller and freely selectable bias force of the sealing ring of the automatic ring, which also operates as a spring, remains. The automatic ring therefore operates for the duration of the switching process and during the equilibrium pressure exclusively as a wiper. This reduces friction and hence also wear and minimizes the required drive power for the slide valve.
The configuration disclosed in DE 10 2005 008 938 B4 has the following disadvantages:
The two assemblies required in addition to the normal swiveling pipe are the shutoff slide valve which must be supported in the feed line about 1 m downstream after the swiveling pipe and the equalization cylinder which must be integrated further downstream in the feed line due to space considerations.
The patented equalization cylinder corresponds in the feed capability to two cylinders connected in parallel, wherein the piston stroke is cut in half compared to conventional equalization cylinders (see DE 42 081 54 A1, FIG. 1). Although the driving hydraulic cylinder is also not installed “in series” following the feed cylinders, but between the two, this equalization cylinder takes up so much space that it can only be accommodated with difficulty and adequately secured on an automotive concrete pump. Moreover, the equalization cylinder is an expensive, complicated and very heavy assembly.
With this in mind, it is an object of the invention to propose a method for continuously feeding pasty masses, which is adapted to more uniformly feed the pasty mass. At the same time, a pump device for feeding pasty masses is proposed which seals the inlet opening particularly well.